Trees can be instrumental in improving air quality and also have very significant implications when it comes to preventing illness and even death, according to a study published last week in the United States.

According to the findings, every year in the United States trees prevent some 850 deaths that were liable to be caused by air pollution, as well as hospitalization of hundreds of people who are exposed to pollutants.

The international journal Environmental Pollution published the findings of the study, conducted by the U.S. Forest Service in cooperation with researchers from the Davey Institute environmental organization. They focused on the contribution of trees in prevention of air pollution, and on the health-related and economic implications of that phenomenon.

According to calculations, in a single year trees in the United States prevent some 17.4 million tons of air pollutants, among them nitrogen dioxide, ozone, sulfur dioxide, and other particulate matter. This is only an estimate, however, based on assumptions regarding the number of trees and their ability to absorb pollutants.

The economic ramifications of reducing pollution, in terms of savings in medical expenditures, is estimated at $6.8 billion a year. In addition to averting hundreds of deaths caused by pollution, tree cover annually prevents some 670,000 U.S. cases of serious respiratory problems that require hospitalization, as well as 430,000 cases of asthma attacks and the loss of 200,000 school days (an achievement that many students may not be very enthusiastic about), according to the study.

Trees have two principle mechanisms for reducing air pollution. The trunk, foliage and branches absorb fine particulate substances from the air, and the leaves absorb various gases.

The fine particles are considered a main cause of morbidity and mortality from air pollution. The gases include nitric acids that create concentrations of ozone in chemical reactions that take place at low altitudes in the atmosphere. This ozone is considered the second greatest health risk when it comes to pollution.

The researchers say that air pollution is reduced in rural areas with a greater number of trees, but the main benefit in terms of health and economics is actually seen in urban areas with far larger populations.

The study did not take into account the amount of pollution reduced in rural areas that could have reached urban centers as well. Nor did it focus on the benefits of preventing pollution damage to crops. Thus, the benefit of trees is even greater than reported in the new study.

When we examine the contribution of trees to reducing air pollution overall, on a national basis it is only a few percentage points. But there are areas where trees can reduce pollution by 5 percent and even more. When it comes to a single street, for example, a row of trees may significantly lower the air pollution from a busy traffic artery nearby, which is of course of great significance to anyone living and working in the vicinity.

While residents in various cities around the world most frequently fight the felling of trees by authorities seeking to make room for houses and roads, this study shows that saving these trees not only adds beauty to the lives of residents, but also helps them protect their health.